There is a kind of antennas, that is, automatic tracking antennas either with a four-axis drive system consisting of an AZ (azimuth) drive axis, an EL (elevation) drive axis, a Cross-EL (cross-elevation) drive axis and a POL (polarization) drive axis, or with a three-axis drive system consisting of an AZ drive axis, an EL drive axis and a POL drive axis. In particular, satellite tracking antenna apparatuses are needed to have mechanical strength that can be secured even under severe vibration conditions, and are needed to have long operating life and high reliability. Furthermore, being low in cost, small in size and low in weight is demanded (for example, see Patent Literature 1).
In maintaining of antennas, visual inspection is conducted to determine whether or not an antenna is in abnormal conditions by checking the appearance of the antenna. Patent Literature 2 discloses a method of performing maintenance by detaching units of an antenna with a three-axis drive system consisting of an AZ drive axis, a Cross-EL drive axis and an EL drive axis. Additionally, a visual inspection apparatus that uses a camera to capture an image of an object to be inspected and uses this captured image to inspect the object is generally known. In using such a visual inspection apparatus, users are required to determine whether or not an antenna is in abnormal conditions by viewing. In other ways, in the case of automatic detection of abnormal conditions, it is needed, for example, to capture an image of an object to be inspected that is in a normal state in advance, to execute image-processing on the image data captured in advance and image data of the object that is captured when visual inspection is conducted, and to determine whether or not the object is in abnormal conditions based on prescribed determination criteria.
For example, Patent Literature 3 discloses an appearance inspection apparatus that displays on a monitor an image of an object to be inspected captured by a CCD camera to allow observation and inspection of the state of the object. Patent Literature 4 discloses an image processing device that has detection means for detecting image information regarding a test object, detects image information regarding a predetermined standard detection target that is used as the test object, obtains difference data that corresponds to differences from image information that is detected in advance regarding the predetermined standard detection target, and displays image information that is based on the difference data.